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A 20-year-old San Diego man died Sunday morning after sustaining serious injuries in a fireworks-related accident, according to the Riverside County Coroner.

William Calabrese of Pacific Beach was injured Friday afternoon near The Diamond in Lake Elsinore, home of the Single A affiliate of the San Diego Padres.

The coroner's office did not provide more details, saying only that an investigation was underway. The Riverside Press-Enterprise reported that Calabrese suffered burns over 90 percent of his body in the accident, which burned two other people, including a Cal/Fire Riverside County fire inspector.

The three were preparing a fireworks show for the Lake Elsinore Storm minor league baseball game, the newspaper reported.

Corey McClelland, a friend of Calabrese's parents, said William was an exceptionally bright and driven young man with a variety of interests and hobbies, including glass-blowing and pyrotechnics. His son Michael was close friends with William.

Calabrese, a swimmer, water polo player and Boy Scout, graduated from La Jolla High School in 2010 and was going into his junior year at University of California, Santa Barbara.

"From a pretty young age, he was really interested in pyrotechnics and fire and guns and that was kind of the one thing that we all commented on," McClelland said. "He really loved fireworks and making people happy by looking at something that exploded."

Friends used to joke with Calabrese about his dangerous hobbies, but they never believed he would be seriously hurt while pursuing them.

"He was an Eagle Scout and knew how to deal with fire," McClelland explained. "Both of his parents knew what kind of person he was and even though we all have certain things we worry about as parents, they didn’t want to stop him from doing what he loved."

Around 200 friends and family gathered Sunday night for a vigil at the Pacific Beach Community Church in a prayer garden that Calabrese built for his Eagle Scout project.

In a eulogy he posted to the team's web page, La Jolla High School water polo coach Tom Atwell described the young man as selfless and hardworking. Calabrese had just the prior weekend looked after his former coach's son while Atwell was out of town.

"Willie was an incredible example to all of us," Atwell wrote. "He worked harder than anyone. He loved to laugh. He was open minded, non-judgmental and forgiving. He was the guy you wanted to go into battle with. He always had your back, whether it was in the water or away from the pool. He held his teammates accountable during workouts, but never demanded more from anyone than he himself was willing to do. He understood and exemplified the term selfless and was an incredible example of service to others.

"Willie always did everything to the extreme."

McClelland said the family does not know any more about what caused the accident than has already been reported. They do not expect to learn the details until the investigation has been closed.